Controling the linewidth of a semiconductor laser withphotorefractive phase conjugate feedback

A novel technique for narrowing the linewidth of a single laser diode using photorefractive phase conjugate feedback is presented. The behavior of this system can be modeled by adapting the previously developed theory to include the phase constraints of the phase conjugate external cavity. The experiments show excellent agreement with the model. This technique produces a stable, narrow linewidth in a semiconductor laser. The comparison to the conventional case is discussed     

Megahertz linewidth from a 1.5 ?m semiconductor laser with HeNe laser injection

The linewidth of a 1.5 ?m semiconductor laser has been reduced from > 1 GHz to < 1.5 MHz by injection locking the laser to the low-power narrow-linewidth output from an HeNe laser operating at 1.523 ?m. A collimated-beam power of 750 ?W was obtained in the injection-locked semiconductor laser mode.     

1.52μm,60kHz线宽光纤布拉格反射镜外腔半导体激光器

本文报道1.52μm光纤布拉格反射镜外腔窄线宽半导体激光器的制作和实验结果,已实现光谱线宽60kHz,边模抑制比优于30dB,输出功率>-5dBm,频率稳定度为50MHz。     

Instability of semiconductor lasers due to optical feedback from distant reflectors

We explain an istability occurring in continuously operating lasers due to moderate feedback from distant reflectors. This instability occurs despite the fact that the laser is stable with respect to small deviations from steady-state operation. It is the result of finite phase and carrier number changes caused by fluctuations in spontaneous emission. We predict several properties that agree with recent experimental observations: 1) the instability only occurs when the laser reaches a steady state that maximizes coherent feedback and laser light intensity; 2) the instability vanishes at strong feedback levels; and 3) at moderate feedback levels, the laser will be nearly stable at threshold, but unstable when operated well above threshold. The latter behavior results in a nonlinear "kinked" shape in the light versus current relation.     

Single longitudinal mode operation of the electron-beam-pumped semiconductor laser

The influence of the external and internal resonator parameters on the laser emission spectral and spatial characteristics has been investigated. Single longitudinal mode operation of the electron-beam-pumped visible semiconductor laser with an external resonator has been observed. A single-mode peak power of 0.8 W and beam divergence of less than 3° were achieved.     

Direct observation of Lorentzian lineshape of semiconductor laser and linewidth reduction with external grating feedback

The Lorentzian lineshape of a single longitudinal mode AlGaAs semiconductor laser is directly observed by optical heterodyne detection. A remarkable reduction in the spectral linewidth to less than 50 kHz is achieved with external grating feedback. The experimental linewidth is in reasonable agreement with the theoretical value, which is obtained by finesse calculation of the active Fabry-Perot cavity.     

The linewidth of a mode-locked semiconductor laser caused by spontaneous emission: Experimental comparison to single-mode operation

We experimentally compare the linewidth of the individual modes of an extended cavity semiconductor laser when it operates mode locked and when it operates single mode. We find that the linewidths under these two operating conditions have the same inverse dependence on the average power. Therefore, the coherence length of the mode-locked source is the same as that of the single-mode source despite lower power per mode, much broader total bandwidth, and much higher spontaneous emission noise level in the mode-locked source. It can be inferred from our data that the electric fields of over 1000 consecutive mode-locked pulses are correlated.     

Narrow spectral linewidth 150 mW semiconductor laser with fundamental transverse mode for SHG light source

A highly reliable, narrow spectral linewidth, 150 mW high-power semiconductor laser that oscillates at a wavelength of 860 nm has been developed, by optimising the structure with a 0.7 mu m thick p-cladding layer, a 900 mu m long cavity length, and current-blocking regions near the facets. Stable, fundamental transverse mode operation was obtained up to 230 mW. The spectral linewidth was 5 MHz at 150 mW. stable operation under 150 mW at 50 degrees C was confirmed for more than 2000 h.<>     

The optimal loop gain design for the spectral linewidth reductionin an electrical feedback semiconductor laser

The design of the optimal feedback loop gain for the spectral linewidth reduction in a semiconductor laser with electrical feedback is presented using a model of self-heterodyne type electrical feedback. The results show that the feedback loop gain must be suitably chosen to satisfy the requirement of narrowing linewidth. Due to the influence of AM noise in the feedback process, there is an optimal value for the feedback loop gain to reduce the linewidth for a given feedback condition. The influence of other feedback parameters on the linewidth reduction is also presented     

Characteristics of a semiconductor laser with external feedback

The theoretical analysis of the compound cavity of a semiconductor laser with external optical feedback is conducted. For large optical feedback, the output power from the laser and its oscillation frequency differ from those for small optical feedback. From the rate equations of the compound cavity, the conditions of the laser oscillation are derived in the presence of large optical feedback The dependencies of the output power and the laser oscillation frequency on the external-cavity length are investigated. Some new results involving laser oscillation depending on the external-cavity length are presented. The experimental results are compared with theoretical predictions. The dependence of the laser oscillation on the external-cavity length is qualitatively explained in the present model     

Semiconductor laser linewidth in optical feedback configurations

We present a theoretical analysis for semiconductor laser linewidth, employing optical feedback. This analysis is valid not only for weak feedback, but also for strong feedback including multiple reflections. The experimental result reported so far under a strong feedback condition is well explained.     

Dependence of the linewidth of a semiconductor laser on the modedistribution

A theory and measurements that show the dependence of the frequency noise spectrum and, therefore, of the semiconductor laser linewidth on the mode distribution are presented. The theory is based on rate equations where the linewidth is strongly influenced by the gain saturation coefficients (nonlinear gain). Analytical results are restricted to two modes. Measurements show that the linewidth change of the main mode depends on the wavelength side of the side mode (related to the wavelength mode of the main mode) and the effect decreases with increasing mode separation. Furthermore, the theoretical and measured frequency noise spectra of a three-mode laser are depicted, showing a characteristic resonance peak for certain mode distributions. This property of the frequency noise spectrum is also described by the theory     

Stabilised PSK transmitter with negative electrical feedback to a semiconductor laser

A method for PSK signal generation using a semiconductor laser in an optical phase-locked loop is presented. The error signal caused by imperfect PM response and phase noise is obtained by optical homodyne detection and fed back to the semiconductor laser. Flat PM response up to approximately 8 MHz is achieved and PSK signal generation is demonstrated.     

The semiconductor laser linewidth due to the presence of side modes

The laser linewidth is evaluated by solving the rate equations for a nearly single-mode laser with two modes. The resulting linewidth contribution due to the presence of side modes is introduced by the nonlinear gain in the laser diode. For weak side modes, the linewidth contribution is proportional to the third power of the side mode intensity. A linewidth contribution of about 20 MHz for a side-mode power of 100 μW has been found experimentally for a 1.3-μm buried-heterostructure laser     

Dynamics of a multimode semiconductor laser with optical feedback

A new model of a multi-longitudinal-mode semiconductor laser with weak optical feedback is proposed. This model generalizes the well-known Tang-Statz-deMars equations, which are derived from the first principles and adequately describe solid-state lasers to a semiconductor active medium. Steady states of the model and the spectrum of relaxation oscillations are found, and the laser dynamics in the chaotic regime of low-frequency fluctuations of intensity is investigated. It is established that the dynamic properties of the proposed model depend mainly on the carrier diffusion, which controls mode-mode coupling in the active medium via spread of gratings of spatial inversion. The results obtained are compared with the predictions of previous semiphenomenological models and the scope of applicability of these models is determined.

     

Spectral linewidth of external cavity semiconductor lasers with strong, frequency-selective feedback

The spectral linewidth of 1.5 ?m external cavity semiconductor lasers is investigated. For nonzero intermediate facet reflectivity, detuning from exact resonance is found to reduce linewidths substantially for strong, frequency-selective feedback. A 10 cm cavity gives linewidths below 1 kHz, while coherent systems requirements will be met by cavities under 2.5 cm.     

Dynamical behavior of a semiconductor laser with filtered externaloptical feedback

We report on a theoretical analysis of the dynamical performance of a semiconductor laser under the influence of delayed weak filtered external optical feedback. The filter widths considered range from 1 to 100 GHz. The analysis concentrates on the well known low-frequency fluctuations (LFFs) regime, in which LFFs occur in the absence of filtering. As expected, filtering the feedback light stabilizes the system in general. LFF can already be suppressed for moderately broad filters (25-50 GHz). In that case, the system was found to operate on the maximum gain mode with a small amplitude limit cycle. We show how the filtering can, in principle, be used for targeting the laser on the maximum gain mode     

FM noise and linewidth reduction in semiconductor laser weakly coupled to a single-mode fibre resonator

Optical feedback effects on spectral properties of an AlGaAs semiconductor laser weakly coupled to a single-mode fibre resonator with a Fabry-Perot transmission bandwidth of 15 MHz are reported. FM noise spectrum, linewidth and resonator output measurements are found to be in good agreement with theory.